Abstract: Scale formation during the liquefaction of lower ranking coals and similar carbonaceous materials is significantly reduced and/or prevented by pretreatment with carbon dioxide. The carbon dioxide pretreatment is believed to convert the scale-forming components to the corresponding carbonate prior to liquefaction. The pretreatment is accomplished at a total pressure within the range from about 14 to about 68 atmospheres and a carbon dioxide partial pressure within the range from about 14 to about 34 atmospheres. Temperature during pretreatment will generally be within the range from about 100.degree. to about 200.degree. C.

Abstract: A novel process, and the compositions of matter formed thereby, wherein Group II-A metals, or compounds thereof, can be ion-exchanged onto coal, preferably a high rank coal, notably a subbituminous or bituminous coal, by soaking the coal in an alkali solution of a Group I-A metal compound sufficient to incorporate said metal compound, or cation portion thereof, into said coal to form ion-exchange sites, and ion-exchanging, and thereby replacing all or a portion, preferably a portion, of the Group I-A metal cations with said Group II-A metals. Enhanced gasification rates are achieved by gasification of the so-treated coal, or composition which contains both the Group I-A and Group II-A metals, as contrasted with a coal composition otherwise similar except that it contains an equal molar quantity of either a Group I-A metal or Group II-A metal, rather than both Group I-A and Group II-A metals.

Abstract: The production of liquid hydrocarbons from coal is significantly enhanced by alkylating or acylating the coal prior to subjecting the coal to liquefaction conditions. The introduction of aliphatic hydrocarbon radicals or acyl radicals, including carbon monoxide, into the coal structure is believed to permit more of the coal to undergo liquefaction at suitable liquefaction conditions. The alkylation or acylation reactions can be conducted in the presence or absence of added or extraneous catalysts.

Abstract: A slurry of coal solids or similar carbonaceous material substantially depleted in mineral-rich particles is prepared for delivery to any desired place of use by introducing particulate coal and a suitable carrier liquid into a slurry preparation zone; passing a stream of slurry from the slurry preparation zone to a liquid-solids separator; returning a concentrated slurry stream from the separator to the slurry preparation zone; and passing a substantially clarified liquid stream from the separator to an elutriation zone, which communicates with and extends downward from the slurry preparation zone, in such a manner as to form an upward directed current in the elutriation zone.